This invention relates to a continuous wave radar system, and is particularly useful in airborne radar altimeters.
In order to minimise detectability of a radar altimeter, the transmitted power is kept to the minimum necessary to achieve an adequate signal-to-noise ratio, i.e. sufficient to obtain a reliable indication of height. It is known in such radar altimeters to vary the transmitted power, increasing the power with the height of the radar altimeter above ground to compensate for the reduction in signal-to-noise ratio. However, the variation of transmitted power can only be achieved with extra power control circuitry, and moreover there is inevitably an upper limit to the power level which can be transmitted. The object of the invention therefore is to provide another means, or an alternative means, of compensating for variations in signal-to-noise ratio in such a radar system.